1. Amphotericin B Dr Pippa Newton, Infectious Diseases Consultant,
Manchester University NHS Foundation Trust

2. Intended learning outcome
To understand the mechanism of action of amphotericin B
To be aware of the spectrum of activity of amphotericin B
To understand the pharmacokinetics of amphotericin B
To be aware of the clinical indication and dosages of amphotericin B
To be aware of the adverse events associated with amphotericin B therapy

3. Introduction
Amphoterin B, the first systemic antifungal, was introduced in 1958
It’s a natural product from the actinomycete Streptomyces nodosus
It offers potent, broad-spectrum antifungal activity against yeasts, moulds and the dimorphic fungi
It’s a large molecule with both hydrophobic and hydrophilic portions (amphiphatic)
It has a molecular weight of 924 g/mol

4. Structure of amphotericin B
Chemical properties
Amphoteric
Reacts as an acid as well as a base
Polyene
Many double bonds
Macrolide
Contains large lactone ring
Lactone
Multiple ketone and hydroxyl groups

5. Mechanism of action Adler-Moore et al. Med Mycol. 2016;3:1:223-231
Amphotericin B binds fungal membrane ergosterol causing:
Increased membrane permeability and
Creation of transmembrane channels (pores)
Resulting in:
Leakage of monovalent ions (K+, Na+, H+, and Cl-),
Leakage of macromolecules from fungal cell
Other mechanisms
Stimulates fungus to produce oxygen radicles
Modulation of macrophage activity
Stimulates pro-inflammatory cytokines
Reactive oxygen intermediates
Nitric oxide
Eventually cell death
Adler-Moore et al. Med Mycol. 2016;3:1:

6. Amphotericin B formulations
“Conventional”
Amphotericin B deoxycholate (AmB-d)
Newer (lipid-based) formulations
Liposomal amphotericin B (L-AmB)
Amphotericin B lipid complex (ABLC)
Amphotericin B colloidal dispersion (ABCD)
Many others

7. Newer amphotericin B formulations
Advantages:
Fewer side effects: lipid vehicle acts as reservoirs, reducing binding to human cells
Improved tolerability
Altered tissue penetration – more in liver, spleen and brain, less in lung and kidneys
Reduced toxicity (esp. nephrotoxicity and anaemia)
However, compared to AmB-D these formulations are less potent by mg dose

8. Newer amphotericin B formulations
Macrophage
Liposome
Lysosome
Fusion
Liposome
degradation
Endocytosis
Endocytic
vesicle
Release from
macrophage
Release in blood
compartment

9. Spectrum of activity
Amphotericin B is one of the most potent antifungal agents, demonstrating activity against:
Moulds
Yeasts
Dimorphic fungi

10. Spectrum of activity of Amphotericin B compared to triazoles
Fungi
Amphotericin B
Fluconazole
Itraconazole
Voriconazole
Posaconazole
Candida albicans
+++
Candida lusitaniae -
Candida krusei
+/-
Cryptococcus spp ++
Aspergillus fumigatus
Aspergillus terreus
Blastomyces spp +
Coccidioides spp
Histoplasma spp
Sporothrix spp
Chromoblastomycoses
Fusarium spp
Scedosporium spp
Mucorales
Perfect JR Clin Infect Dis. 2010;50:
Pappas PG Clin Infect Dis 2009;48:

11. Resistance Higher MICs to: Intrinsic resistance Acquired resistance
Aspergillus terreus
Aspergillus nidulans
Candida lusitaniae
Scedosporium spp.
Acquired resistance
Very rare
Higher MICs to:
Aspergillus flavus
Fusarium spp.
Scedosporium spp.
Candida krusei
Paecilomyces lilanicus

12. Biopharmaceutical differences of amphotericin B formulations
Characteristics
AmB-d
L-AmB
ABLC
ABCD
Mol % AmB
34%
10%
35%
50%
Lipid configuration
Micelles
Small unilamellar vesicles
Ribbon-Like
Disk like
Diameter (µm)
<0.4
0.08
Dosage (mg/kg)
0.5-1
3-5 5
3-4
Cmax (vs. AmB-d) -
Increased
Decreased
AUC (vs. AmB-d)
Vd (vs. AmB-d)
Similar
Clearance (vs. AmB-d)
Nephrotoxicity
+++
+/-
Infusion toxicity
High
Mild
Moderate
Groll et al . Adv. Pharmacol. 1998;44:

13. Lipid Amphotericin B formulations

14. Pharmacokinetics Bioavailability: All formulations are parental
Distribution: Well distributed in most body compartments
CNS penetration ~0%
Metabolism: t1/2: ~15 days (detectable in urine for at least 7 weeks after last dose)
Protein binging > 90% and is poorly dialyzable
Elimination: Excreted unchanged in urine (21%) and faeces (43%)
Bellmann & Smuszkiewicz: Infections pp1-43

15. Clinical indications First-line indications Other indications
Cryptococcal meningitis
Histoplasmosis
Mucormycosis
Penicilliosis (Talaromyces marneffei infection)
Leishmaniasis
Other indications
Invasive aspergillosis
Invasive candidiasis
Candidaemia
Coccidioidomycosis
Blastomycosis
Phaeohyphomycosis
Sporotrichosis (disseminated)
Oesophageal candidiasis
Nett & Andes. Infect Dis Clin N Am. 2016;
Indications in red are the main first line indications where amphotericin B is the leading product.

16. Dosages Amphotericin B deoxycholate Amphotericin B Liposomal Adults:
Adults: 0.7-1mg/kg/day
Paediatrics: 0.7-1mg/kg/day
Amphotericin B Liposomal
Adults:
Empiric therapy in neutropenia: 3 mg/kg/day
Systemic infections: 3-5 mg/kg/day
Cryptococcal meningitis: 6 mg/kg/day
Paediatrics: same weight-based dosing

17. Adverse events Acute infusion-related reactions Nephrotoxicity
Nausea, vomiting, rigors , fever, hyper/hypotension, and hypoxia
Caused by the effects of amphotericin B on pro-inflammatory cytokine production
Nephrotoxicity
34-60% of patients
Due to:
Vasoconstriction
Direct damage to the distal tubule cell membranes
Results:
Loss of electrolytes
Impaired urinary acidification and concentration
Renal tubular acidosis
Loo et al. Expert Opin Drug Saf. 2013;12:
Groll et al. Adv Pharmacol. 1998; 44;

18. Other adverse events Very common ( ≥1/10) Common (≥1/100 to <1/10)
Nausea, vomiting
Hypotension
Hypokalaemia
Transient renal function test abnormalities (azotemia, hyposthenuria, renal tubular acidosis and nephrocalcinosis)
Chills
Common (≥1/100 to <1/10)
Anaemia
Hypomagnesemia
Headache
Diarrhoea
Liver function test abnormalities
Injection site pain (with or without phlebitis or thrombophlebitis)
Acute renal failure
Bone or other pain (AmBisome)
Rare ( ~ 1/1000)
Anaphylaxis
Fungizone SPC: emc last updated 29-Nov-2016

19. Contraindication Known hypersensitivity to amphotericin B
Unstable/moderately renal dysfunction, unless unavoidable.

20. Tips on administering amphotericin B
Use a central line if possible for AmB-D, as phlebitis common – not so important for lipid- AmB.
Set the infusion up and run in about 10 ml, and then stop for mins to check for anaphylaxis – a ‘test dose’ unnecessary and delays therapy.
Slower infusions reduce acute infusion-related side effects (> 2 hours for lipid formulations, > 4 hours for AmB-d)
Pre-loading with N/saline (500-1,000 mL) reduces renal dysfunction
Check renal function daily for first 4-5 days then, 3x weekly
Avoid other nephrotoxic drugs, especially aminoglycosides and frusemide
Check K+ at least 2x/week and mg++ weekly, if possible.
Amiloride 5 mg daily, may reduce K+ loss.
Check Hb at 7, 14 and 21 days – may need transfusion
Avoid giving hydrocortisone for infusion-related side effects, if possible. Use acetaminophen/paracetamol, or low dose opiate.
Khoo et al. J Antimicrob Chemother. 1994; 33:
Khoo et al.

21. Conclusion
Amphoterin B, the first systemic antifungal, was introduced in 1958
It offers potent, broad-spectrum antifungal activity but is associated with significant renal toxicity and infusion reactions
Lipid-based amphotericin B formulations were introduced in the 1990s and maintain the potent, broad-spectrum activity of the deoxycholate formulation with less toxicity
Drug of choice for the vast majority of life-threatening systemic fungal infections
Treatment of mycoses in pregnant women as triazole class are considered teratogenic